Reverse-psuedohyperkalemia sounds like it might be Elon Musks new child but it's a real thing. The fragility of excessive leukemic white cells combined with a possible cellular sensitivity caused by Lithium Heparin causes an increase in extracellular potassium upon any excessive mechanical manipulation/stress such as riding along in the tube system or centrifuging. One way of combating this is to draw a serum tube rather than a plasma tube (LiHep) and maybe even hand deliver it to our smiling MLS faces. Of course this does't work in every R-PK+ case, and the only way to get an accurate potassium may be to order a whole blood K+. 

It's called reverse-pseudohyperkalemia because the K+ is falsely elevated in plasma rather than serum. When K+ is falsley elevated in serum rather than plasma, it is simply known as psuedohyperkalemia. 

Unlike reverse-psuedohyperkalemia which, as previously touched upon, usually results as a consequence of leukocytosis, regular pseudohyperkalemia usually results as a consequence of thrombocytosis. So if a patient has a very high platelet count, you very well may see abnormal K+ results when testing using serum. 

(We just had a patient with a 3 MILLION /mm3 PLT count. Yeah they had to have numerous plateletpheresis sessions...)  

Also, whereas in reverse-pseudohyperkalemia the causative agent of excess K+ is fragile leukemic white blood cells lysing, high K+ arises in pseudohyperkalemia (serum tubes) as a result of potassium egress during the platelet activation stage of clotting.